1. Field of the Invention
The present invention relates to an image display device and an image displaying method and more specifically to an image display device, and an image displaying method thereof, such as a monitor and a data projector comprising a matrix type display device (hereinafter referred to simply as a display panel) such as a liquid crystal panel, a digital mirror device (DMD) and a field emission display (FED) to which any one of a plurality of image signals whose synchronizing signal frequency is different is inputted.
2. Description of the Related Art
FIG. 1 is a diagram showing a conventional image display device. In the figure, the image display device comprises an image signal inputting terminal 1, an A/D converter 2, a display panel 4, a horizontal synchronizing signal inputting terminal 5, a vertical synchronizing signal inputting terminal 6, a clock generator 9, an image signal processing circuit 103 and a driving circuit 110. The reference symbol (HD) denotes a horizontal synchronizing signal, (VD) a vertical synchronizing signal, (CK) a clock signal and (DS1) a signal for driving the display panel 4.
An operation the unit will be explained below. In the same time when the horizontal synchronizing signal HD is inputted to the horizontal synchronizing signal inputting terminal 5, the vertical synchronizing signal VD is inputted to the vertical synchronizing signal inputting terminal 6. An image signal synchronized with the horizontal synchronizing signal HD and the vertical synchronizing signal VD is inputted to the image signal inputting terminal 1.
The clock generator 9 generates the clock CK of a predetermined frequency based on the horizontal synchronizing signal HD inputted from the horizontal synchronizing signal inputting terminal 5. The clock CK generated by the clock generator 9 is supplied to the A/D converter 2, the image signal processing circuit 103 and the driving circuit 110.
The A/D converter 2 samples the image signal inputted from the image signal inputting terminal 1 with timing of the clock CK to convert into digital image data.
The digital image data Di converted by the A/D converter 2 is inputted to the image signal processing circuit 103 to undergo a certain image signal processing. The digital image data Di processed by the image signal processing circuit 103 is inputted to the display panel 4.
Meanwhile, the driving circuit 110 generates the driving signal DS1 for driving the display panel 4 based on the horizontal synchronizing signal HD inputted from the horizontal synchronizing signal inputting terminal 5 and the vertical synchronizing signal VD inputted from the vertical synchronizing signal inputting terminal 6.
The display panel 4 displays an image of the image data outputted from the image signal processing circuit 103 based on the driving signal DS1 outputted from the driving circuit 110.
Because the conventional image display device has been constructed as described above, there has been a problem that the image cannot be displayed normally on the display panel 4, or the display is so disturbed that an user is unable to recognize the type of the inputted image, when the frequency of the inputted horizontal synchronizing signal HD is higher than a predetermined frequency which enables to display on the display panel 4. Therefore, the frequency of the horizontal synchronizing signal of the inputted image signal cannot be changed to the frequency which enables to display on the display panel 4 while watching the image displayed on the display panel 4.
More specifically, there has been a problem that when the horizontal frequency of synchronizing signal is erroneously set at a frequency higher than the horizontal frequency of synchronizing signal which enables to display on the image display device in changing resolution of the image or refresh rate by a personal computer connected to the display device, it has been impossible to return the frequency to one before the change or to reset to the frequency or below which enables to display on the display panel 4 while watching the screen because no image is displayed on the display panel 4 or the display is so disturbed that the image cannot be recognized after when the setting has been changed.
Accordingly, it is an object of the invention to solve the above-mentioned problems by providing an image display device, and an image displaying method thereof, which enables to confirm what type of image signal is being inputted and to display an image to a degree which enables to reset the horizontal (or vertical) frequency of synchronizing signal readily to the optimum frequency even when an image signal of horizontal (or vertical) frequency of synchronizing signal which cannot be displayed on a display panel is inputted.
The invention provides an image display device comprising a clock generator for generating clock having a frequency and phase based on a synchronizing signal of an image signal; an A/D converter for sampling the image signal with the clock to convert into a digital image signal; synchronizing frequency discriminating means for discriminating whether or not the synchronizing signal has a frequency higher than a preset frequency; synchronizing signal processing means for reducing the synchronizing signal based on the discrimination result of the synchronizing frequency discriminating means and outputting a modified synchronizing signal; image signal processing means for reducing the digital image signal on the basis of the modified synchronizing signal to output a reduced digital image signal; and a display unit for displaying an image corresponding to the reduced digital image signal outputted from the image signal processing means.
The invention also provides an image display device comprising a clock generator for generating clock having a frequency and phase based on a synchronizing signal of an image signal; and A/D converter for sampling the image signal with the clock to convert into a digital image signal; synchronizing frequency discriminating means for discriminating whether or not the synchronizing signal has a frequency higher than a preset frequency; synchronizing signal processing means for reducing a horizontal synchronizing signal by removing its portions corresponding to either one of odd or even lines in an n-th field (n is a positive integer) and the other one of the odd or even lines in an n+1-th field based on the discrimination result of the synchronizing frequency discriminating means and outputting a modified synchronizing signal; a memory capsule of storing data of at least one field of the digital image signal; image signal processing means for reducing the digital image signal on the basis of said modified synchronizing signal to write, into the memory, a reduced signal corresponding to the n-th field and a reduced signal corresponding to the n+1-th field and for reading out the reduced signals stored in the memory in predetermined order of lines to combine the reduced signals to obtain a combined digital image signal, and for outputting the combined digital image signal; and a display unit for displaying an image corresponding to the composed digital image signal outputted from the image signal processing means.
The invention also provides an image displaying method for displaying an image on a display unit comprising steps of discriminating whether or not a synchronizing signal of the image signal has a frequency higher than a preset frequency; reducing the image signal based on the discrimination result to output a reduced image signal; and displaying an image corresponding to the reduced image signal on the display unit.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.